1. Field of the Invention
The present invention relates to a rotation transfer mechanism for transferring a torque of a rotatable ring to a driven member, and also relates to a zoom camera (a zoom-lens-equipped camera) which incorporates such a rotation transfer mechanism.
2. Description of the Related Art
Zoom cameras having a zoom lens which incorporate a zoom viewfinder and/or a zoom flash that operates in association with a variation of the focal length of the photographing (imaging) optical system are known in the art. It is often the case that in such zoom cameras a rotatable ring which drives the photographing optical system also drives the zoom viewfinder and/or the zoom flash. However, in a particular type of zoom camera in which the photographing optical system is not only driven in a zooming range (a range between wide-angle extremity and telephoto extremity) but also capable of being retracted, the zoom viewfinder and/or the zoom flash must be made not to be associated with the photographing optical system when the photographing optical system is in a state between a ready-to-photograph state and a fully-retracted state. Conventionally, to cancel the association of the photographing optical system with the zoom view finder and/or the zoom flash, a rotation transfer mechanism (drive transfer system) for transferring a torque of the rotatable ring to the zoom viewfinder and/or the zoom flash needs to be provided with an idle running section for disengaging the zoom viewfinder and/or the zoom flash from the rotatable ring. However, it is desirable that the rotation transfer mechanism not be provided with such an idle running section from the viewpoint of miniaturization of the zoom viewfinder and/or the zoom flash and the accuracy in driving the zoom viewfinder and/or the zoom flash. For instance, in the case where the rotation transfer mechanism includes a cam, the size of the cam increases if the cam is provided with the idle running section. In this case, even if the cam is provided with the idle running section without increasing the size of the cam, the shape of the remaining section of the cam is limited, which makes it difficult to obtain an ideal cam shape or contour.
Similar problems arise not only in rotation transfer mechanisms of such zoom cameras but also in rotation transfer mechanisms of other devices in which a rotatable ring and a driven member are made to be associated with each other when the rotatable ring is positioned in a predetermined range of rotation thereof relative to the driven member and in which the rotatable ring and the driven member are made not to be associated with each other when the rotatable ring is positioned outside the predetermined range of rotation thereof relative to the driven member.